Article 967 - Distributor Vacuum Thermal Sensing Unit

TSB #56 - December 16, 1966
(1967 Vehicles So Equipped)

This article supersedes the Thermal Sensing Unit information given in the 1967 car preliminary Shop Manuals.

On some Thermactor-equipped engines, the distributor vacuum is obtained from either the intake manifold or carburetor vacuum port. An application table is given in Fig. 1.

The thermal sensing valve, installed in the heater water system, will control the source of the distributor vacuum pickup. Normally, the distributor will operate on carburetor vacuum, but at 230-degrees F (approximate) engine coolant temperature, the thermal sensing valve will close the carburetor vacuum pickup and open the intake manifold full vacuum pickup. Thus, under hot idle conditions, the distributor will have an increased advance, due to increased vacuum, causing an increase in engine idle speed.

This helps to reduce engine operating temperature under hot idle conditions.



    1. Drain the cooling system.
    2. Remove the air cleaner.
    3. Disconnect the heater hose and the three vacuum lines at the Thermal Sensing Unit.
    4. Remove the Thermal Sensing Unit.

    1. Coat the Thermal Sensing Unit threads with water-resistant sealer and install the Thermal Sensing Unit and torque it to 23-30 ft.-lbs.
    2. Coat the heater hose fitting with water-resistant sealer. Install the heater hose.
    3. Refer to Illus. S1154-A and install the vacuum lines.
    4. Fill the cooling system. Start the engine and check for leaks.
    5. Install the air cleaner.

289Mustang, CougarThermactor & Air Conditioning
390Fairlane, Comet, MercuryThermactor & Air Conditioning
390, 428ThunderbirdThermactor
428MercuryThermactor & Air Conditioning
428 PoliceFord, MercuryAir Conditioning